1. Field of the Invention
The present invention relates to an inkjet recording apparatus, and more particularly to a technology for preventing ink from bleeding.
2. Description of the Related Art
Conventional printing processes are well known in which printing is carried out onto a print medium by employing an ultraviolet (UV) curable ink, and the ink is prevented from bleeding by causing the ink to harden by irradiating UV light onto the ink after the ink has been deposited on the print medium.
Japanese Patent Application Publication No. 2003-11334 discloses a device in that a UV light source is arranged integrally with an ink ejecting head along the travel direction of the head. The ink ejected from the head is caused to harden by irradiating UV light from the UV light source onto the ink in a recorded region that has been recorded in the previous scan.
Japanese Patent Application Publication No. 2003-11343 discloses a technique in that, when an ink ejection operation has been performed, the ejected ink is hardened by irradiating UV light before the next ink ejection operation in order to prevent ink bleeding and recording irregularities.
In Japanese Patent Application Publication No. 2002-187918, paragraph “0104”, there is a description that the ink should be caused to harden before the ink permeates into the recording medium (the recording paper).
Japanese Patent Application Publication No. 2003-89198 discloses that a light guide that irradiates setting light for provisional curing is arranged in the vicinity of an inkjet nozzle. After the ink has been provisionally cured by means of the setting light from the light guide, the ink is durably fixed by another light source.
Japanese Patent Application Publication No. 2003-145741 discloses a fixed UV light source of a size that can cover the range scanned by a head.
In Japanese Patent Application Publication No. 2003-192943, there is a description that a time period from the ink ejection to the UV irradiation is determined. Japanese Patent Application Publication No. 2003-192943 also discloses a line type head having a length corresponding to the maximum width of the print medium.
In Japanese Patent Application Publication No. 2003-191594, there is a description that various irradiation conditions, such as the light irradiation time, irradiation intensity, irradiation surface area, and angle of incidence, are adjusted in accordance with the type of the print medium, the type of the ink, the viscosity of the ink, and the like.
Japanese Patent Application Publication No. 60-132767 and U.S. Pat. No. 6,092,890 disclose a UV light source arranged integrally with a head.
U.S. Pat. No. 6,145,979 discloses a device in that light is guided from the outside of a head to the vicinity of the head through mirrors or an optical fiber, and the device irradiates the light with the movement of the head unit.
The above-described conventional apparatuses are classified into any one of the followings:
(1) a light source for curing ink is fixed to an inkjet recording apparatus, and the light source irradiates light onto the whole of the irradiation object as the irradiation object moves;
(2) a light source for curing ink is fixed to a head, and the light source irradiates light onto the irradiation object as the head moves for scan; or
(3) a light source for curing ink guides light to the head from the outside of the head through some kind of device and/or method, and the light source irradiates light onto the irradiation object as the head moves for scan.
All of the above-described conventional apparatuses adopt the same approach in that the light is directed onto the whole of the print medium. The conventional apparatuses are devised in order that the light is irradiated as immediately as possible after printing so that the print ink can be prevented from bleeding. More specifically, the above-described conventional inkjet recording apparatuses irradiate UV light immediately after the ink has been ejected toward the print medium so that the ink is prevented from bleeding; however, they may involve the following problems.
(1) In order to irradiate the UV light immediately after the ink has been ejected, it is necessary to arrange a light source or a member for guiding the UV light in the vicinity of the head. When the UV light is to be irradiated onto the entire print region for causing the ink to harden, high energy is required and hence the light source unit can be large in size.
(2) When the UV light is irradiated onto the print medium, the UV light can reach the peripheral areas by the diffuse reflection at the irradiation position. If the irradiation position of the UV light is brought close to the print position so that the ink can be prevented from bleeding, the diffuse reflected UV light may cause the ink to harden inside the head before the ink is ejected. Thus, there is a possibility of head blockages.
(3) If a laser diode having good light emission efficiency is used in order to save energy in the inkjet recording apparatus, there is a possibility that the energy may not be sufficient to cause the ink to harden over the whole print medium depending on the speed of conveyance of the print medium, since the luminous energy emitted from the laser diode may be smaller than that from other devices, such as an electric discharge tube.